The simple sacral dimple: diagnostic yield of ultrasound in neonates

Although spinal cord tethering is known to be associated with certain clinical syndromes and cutaneous stigmata, its incidence in healthy infants with simple sacral dimples has not been thoroughly evaluated.

Our objective was to determine the frequency of tethered cord in otherwise healthy patients with simple sacral dimples.

We reviewed the lumbar spine US reports of all healthy neonates referred for a simple sacral dimple during a 12-year period at two children's hospitals. A sonogram was considered abnormal for a conus medullaris terminating below the L2-L3 disc space, decreased conus or nerve root motion, an abnormal filum terminale, or for the presence of an intraspinal mass, osseous dysraphism, or a sinus leading to the thecal sac. The medical records of patients with abnormal screening sonograms were reviewed to determine the final clinical outcome.

During the study period 3,991 infants underwent screening sonography. Of these, 107 were excluded because of the presence of other medical conditions. Of the remaining 3,884 healthy infants, 133 (3.4%) had an abnormal sonogram. Five (0.13%) of these infants were lost to follow-up; 52 subsequently had normal follow-up imaging; 49 had a low conus without other signs of tethering; 18 had a fatty filum; 2 had decreased conus motion; 2 had both a low conus and a fatty filum. None of these infants underwent surgery. Only the remaining 5/3,884 (0.13%) infants underwent surgical intervention (95% CI: 0-0.27%), and 4/5 were found to have a tethered cord intraoperatively.

The risk of significant spinal malformations in asymptomatic, healthy infants with an isolated simple sacral dimple is exceedingly low.